Merge pull request #4017 from gmbecker/PR_rmagic2

Add REPL-like printing of final/return value to %%R cell magic

IPython/extensions/rmagic.py

@@ -184,20 +184,28 b' class RMagics(Magics):'
 
     def eval(self, line):
         '''
-        Parse and evaluate a line with rpy2.
-        Returns the output to R's stdout() connection
-        and the value of eval(parse(line)).
+        Parse and evaluate a line of R code with rpy2.
+        Returns the output to R's stdout() connection, 
+        the value generated by evaluating the code, and a
+        boolean indicating whether the return value would be
+        visible if the line of code were evaluated in an R REPL.
+        
+        R Code evaluation and visibility determination are
+        done via an R call of the form withVisible({<code>})
+        
         '''
         old_writeconsole = ri.get_writeconsole()
         ri.set_writeconsole(self.write_console)
         try:
-            value = ri.baseenv['eval'](ri.parse(line))
+            res = ro.r("withVisible({%s})" % line)
+            value = res[0] #value (R object)
+            visible = ro.conversion.ri2py(res[1])[0] #visible (boolean)
         except (ri.RRuntimeError, ValueError) as exception:
             warning_or_other_msg = self.flush() # otherwise next return seems to have copy of error
             raise RInterpreterError(line, str_to_unicode(str(exception)), warning_or_other_msg)
         text_output = self.flush()
         ri.set_writeconsole(old_writeconsole)
-        return text_output, value
+        return text_output, value, visible
 
     def write_console(self, output):
         '''
@@ -413,13 +421,16 b' class RMagics(Magics):'
             In [9]: %R X=c(1,4,5,7); sd(X); mean(X)
             Out[9]: array([ 4.25])
 
-        As a cell, this will run a block of R code, without bringing anything back by default::
+        In cell mode, this will run a block of R code. The resulting value
+        is printed if it would printed be when evaluating the same code 
+        within a standard R REPL.
+        
+        Nothing is returned to python by default in cell mode.
 
             In [10]: %%R
                ....: Y = c(2,4,3,9)
-               ....: print(summary(lm(Y~X)))
-               ....:
-
+               ....: summary(lm(Y~X))
+       
             Call:
             lm(formula = Y ~ X)
 
@@ -580,14 +591,20 b' class RMagics(Magics):'
         try:
             if line_mode:
                 for line in code.split(';'):
-                    text_result, result = self.eval(line)
+                    text_result, result, visible = self.eval(line)
                     text_output += text_result
                 if text_result:
                     # the last line printed something to the console so we won't return it
                     return_output = False
             else:
-                text_result, result = self.eval(code)
+                text_result, result, visible = self.eval(code)
                 text_output += text_result
+                if visible:
+                    old_writeconsole = ri.get_writeconsole()
+                    ri.set_writeconsole(self.write_console) 
+                    ro.r.show(result)
+                    text_output += self.flush()
+                    ri.set_writeconsole(old_writeconsole)
         
         except RInterpreterError as e:
             print(e.stdout)